This invention relates to a safety contact rail for power-driven devices and the like or a safety contact element, as a switch hose and the like, with an elastic hollow section within which there are a plurality of strip-like electrically conductive projections that are isolated from one another by nonconductive cross sections, the conductive projections generating a switching pulse upon coming into contact with one another.
DE 39 21 533 A1 describes a safety contact rail of the stated kind for power-driven devices in which there are two strip-like electrically conductive projections and an also electrically conductive mating surface in the interior of a hollow section. Reliable contact is said to be provided through this practice. Further, there is said to be a post-deformation travel after pulse initiation as a result of this triangular arrangement.
It is an object of the present invention to-improve the safety contact rail of the stated type or a safety contact element in such a fashion that there is always a redundant contact, regardless of the direction in which the initiating force acts on the safety contact rail or safety contact element. The object of the invention is achieved by virtue of the fact that there are at least four strip-like electrically conductive projections and that these projections are identical in form and arranged evenly distributed within the hollow section. The cross-sectional surfaces of the projections are preferably selected and arranged such that they run in pointwise symmetric fashion relative to the central axis of the hollow section. It makes no difference from what direction the force is applied to the safety contact rail or safety contact element, because at least two projections are always in contact with one another and generate switching pulses relative to one another.
The cross-sectional surfaces of the projections are shaped such that they can be essentially defined by two right triangles with unequally long legs. They do not, of course, constitute two triangles, but they can be divided into corresponding triangles and described in this way. The large triangles have their hypotenuses adjoining the inner periphery of the hollow section or form in themselves part of the periphery of the hollow sections, the hypotenuses not being designed as straight lines but being curved in correspondence with the inner periphery of the hollow section or with the outer periphery of the hollow section. Adjacent to the large triangles are small triangles having their long legs adjacent to the long legs of the large triangles, so that the short legs of the large triangles and of the small triangles form a straight line. For the further improvement of contact, strip-like lips are attached to the vertices between the hypotenuses and the short legs of the small triangles, which lips run substantially in prolongation of the hypotenuses of the small triangles and overhang the surfaces of the short legs of the small triangles. As a result of this design of the cross-sectional surfaces of the projections, a cavity is created in the interior of the hollow section along the safety contact rail or safety contact element, which cavity is defined by a square cross-sectional area in the center, on whose lateral surfaces hollow lanes are formed adjacent to each edge, which hollow lanes are constricted by the strip-like lips, further hollow lanes being adjacent to these hollow lanes and angularly offset therefrom and reaching to the nonconductive cross section of the hollow section. The choice of a small contact area, in particular via the strip-like lips, was deliberate. It leads to a high contact pressure, which contributes to self-cleaning of the contact surfaces.
In order to improve the conductivity in the cross-sectional areas of the projections, electrically conductive wires or stranded conductors made of metal, carbon fibers or graphite fibers can be embedded.
The safety contact rail or safety contact element can have two unlike nonconductive regions. First, the strip-like projections can be arranged inside a shell with annular cross section, the shell being fabricated from nonconductive material. Second, the cross sections of the strip-like projections themselves can be part of the outer periphery of the hollow section, nonconductive portions being provided between them. In one case, the outer periphery of the hollow section is completely nonconductive because it is surrounded by the nonconductive shell, while in the other case there are conductive and nonconductive portion-wise regions that form the outer periphery of the hollow section. In the first case cited, with shell, the section is also insensitive to external effects such as moisture and the like, because no xe2x80x9cforeign contactxe2x80x9d can occur.
The safety contact rail or safety contact element is advantageously fabricated with the elastic hollow section made of extrudible material, in particular rubber or polymers, and fabricated in one piece, including the embedded wires or stranded conductors if applicable, preferably as an endless section in an extruder, so that a homogeneous section is produced. Hollow sections with six or eight, or even more, projections can also be fabricated and used.
By virtue of the fact that in every case there are four conductive cross sections along a safety contact rail or safety contact element, various connections or circuits can be created. If the safety contact rail or safety contact element has one end connected to a transmission line, adjacent electrically conductive cross sections at the opposite end can be connected to one another in parallel or diagonal fashion by flexible contact bridges, a two-wire or four-wire configuration being selectable at the connection end. If a two-wire configuration is chosen, the two free cross sections at the connection end are preferably bridged by a resistor or a diode.
The conductive cross sections, however, can also be flexibly connected to one another with four resistors or diodes at the end of the safety contact rail or safety contact element opposite the connection. The connection end is then connected to a four-channel evaluator, that is, to a four-pole connecting line.
For the further explanation of the invention, reference is made to the Drawing, in which exemplary embodiments of the invention are illustrated in simplified form.